TM4C1294NCPDT: PWM signal stays HIGH

Briceag Cosmin

Part Number: TM4C1294NCPDT

Hello,

I try to generate a PWM signal using of the PWMs modules. Basically, the steps involved in configuring the PWM are simple but I end up with a signal which stays permanently on HIGH. Please find below my initialization steps:

ui32SysClock = MAP_SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |

SYSCTL_OSC_MAIN | SYSCTL_USE_PLL |

SYSCTL_CFG_VCO_480), 120000000);

            uint32_t period = ui32SysClock / 250; /*250 Hz*/

            SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
            SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);

            HWREG(GPIO_PORTF_BASE + GPIO_O_LOCK) = 0x4C4F434B;

            GPIOPinConfigure(GPIO_PF0_M0PWM0);
            ROM_PWMClockSet(PWM0_BASE, PWM_SYSCLK_DIV_1);
            GPIOPinTypePWM(PWM0_BASE, GPIO_PIN_0);
            PWMGenConfigure(PWM0_BASE, PWM_GEN_0, PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);
            PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, period);
            PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0_BIT, (period * 10) / 100); /*10%*/


            PWMIntEnable(PWM0_BASE, PWM_INT_GEN_0);
            PWMGenIntRegister(PWM0_BASE, PWM_GEN_0, pwmIsrCh0);
            PWMGenIntTrigEnable(PWM0_BASE, PWM_GEN_0, PWM_INT_CNT_LOAD);
            IntEnable(PWM0_BASE);
            PWMOutputState(PWM0_BASE, PWM_OUT_0_BIT, true);
            PWMGenEnable(PWM0_BASE, PWM_GEN_0);

static void pwmIsrCh0(void)
{
    uint32_t counter_value = (10 * period) / 100 ;

    PWMGenIntClear(PWM0_BASE, PWM_GEN_0, PWM_INT_CNT_LOAD);

    PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0_BIT, counter_value);
}

The ISR is successfully called.

over 6 years ago

0 Bob Crosby over 6 years ago

TI__Guru 72500 points

The first argument of the function GPIOPinTypePWM is the base address of the GPIO port, not the base address of the PWM. Line10 of your code above should look like:

    GPIOPinTypePWM(GPIO_PORTF_BASE, GPIO_PIN_0);

0 Briceag Cosmin over 6 years ago in reply to Bob Crosby

Intellectual 840 points

Hello Bob,

Yes, you are right.
It was just a typo mistake when I copied from code.

The real configuration is like you presented.

0 Bob Crosby over 6 years ago in reply to Briceag Cosmin

TI__Guru 72500 points

The PWM load register which generates the period is only 16 bits. The value you loaded is too large (120,000,000 / 250 = 480,000 or 0x75300). Only the last 16 bits are loaded into the register, 0x5300 or 21,248. The compare value you used for the pulse width 48,000 is less than 16-bits, but since it is greater than the load value, the counter never generates a match condition so the PWM output stays high.

0 Bob Crosby over 6 years ago in reply to Briceag Cosmin

TI__Guru 72500 points

I fixed two other copy errors. Here is the working code.

#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_types.h"
#include "inc/hw_memmap.h"
#include "inc/hw_gpio.h"
#include "inc/hw_ints.h"
#include "driverlib/sysctl.h"
#include "driverlib/gpio.h"
#include "driverlib/pwm.h"
#include "driverlib/interrupt.h"
#include "driverlib/pin_map.h"

//*****************************************************************************
//
// Main 'C' Language entry point.
//
//*****************************************************************************
static void pwmIsrCh0(void);

uint32_t period;

int
main(void)
{
    uint32_t ui32SysClock;

    //
    // Run from the PLL at 120 MHz.
    //
    ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                       SYSCTL_OSC_MAIN |
                                       SYSCTL_USE_PLL |
                                       SYSCTL_CFG_VCO_480), 120000000);

    period = ui32SysClock / 2500; /*2.5 KHz*/

    SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
    GPIOPinConfigure(GPIO_PF0_M0PWM0);
    PWMClockSet(PWM0_BASE, PWM_SYSCLK_DIV_1);
    GPIOPinTypePWM(GPIO_PORTF_BASE, GPIO_PIN_0);
    PWMGenConfigure(PWM0_BASE, PWM_GEN_0, PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);
    PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, period);
    PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0, (period * 10) / 100); /*10%*/
    PWMIntEnable(PWM0_BASE, PWM_INT_GEN_0);
    PWMGenIntRegister(PWM0_BASE, PWM_GEN_0, pwmIsrCh0);
    PWMGenIntTrigEnable(PWM0_BASE, PWM_GEN_0, PWM_INT_CNT_LOAD);
    IntEnable(INT_PWM0_0);
    PWMOutputState(PWM0_BASE, PWM_OUT_0_BIT, true);
    PWMGenEnable(PWM0_BASE, PWM_GEN_0);

    while(true)
    {
    }
}

static void pwmIsrCh0(void)
{
    uint32_t counter_value = (10 * period) / 100 ;
    PWMGenIntClear(PWM0_BASE, PWM_GEN_0, PWM_INT_CNT_LOAD);
    PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0_BIT, counter_value);
}

0 Briceag Cosmin over 6 years ago in reply to Bob Crosby

Intellectual 840 points

Hello Bob,

Thank you for spending time to create this example for me.

Indeed, I found the mistake. Instead of writing "PWM_OUT_0" I wrote "PWM_OUT_0_BIT".

Now it works as expected.

All the best !

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TM4C1294NCPDT: PWM signal stays HIGH